Determining the optimal ropivacaine concentration for spinal anaesthesia during day surgery for anorectal procedures: a dose-finding study.

Ropivacaine is a commonly utilized local anesthetic for spinal anesthesia (SA); however, its optimal concentration for elective anorectal surgery has not been thoroughly estimated. This study investigated the minimum effective concentration (MEC90) of ropivacaine required to achieve successful SA in patients aged 18-65 years undergoing elective anorectal procedures. Fifty-one patients received SA with 1.5 ml of ropivacaine hydrochloride, utilizing a biased coin design and an up-and-down method, commencing at an initial concentration of 0.30% and adjusted in increments of 0.05%. The results demonstrated that the MEC90 of ropivacaine for SA was 0.2482% (3.7320 mg, 95% CI: 0.1500-0.3000%). Moreover, MEC99 was extrapolated to 0.2926% (4.4389 mg, 95% CI: 0.2500-0.3000%) for 1.5 ml. These findings suggest that a concentration of 0.2482% (3.7320 mg) effectively induces SA in 90% of patients, while a higher concentration of 0.2926% (4.4389 mg) may be recommended to achieve a 99% efficacy rate.Clinical trial registration ChiCTR2300074796 ( https://www.chictr.org.cn/ ).